On 29.07.2008, at 18:01, Roland King wrote:
I started over a couple of weeks ago with the new Hillegass book,
trying to make sure I understood things properly this time and of
course I'm now stuck.
I'm at the 'RaiseMan' chapter now. This is where Hillegass
introduces a NSArrayController and its use with an NSTableView. Here
are the major pieces.
MyDocument exposes an 'employees' property, a NSMutableArray, that's
an array of 'Person' objects, each with a personName and
expectedRaise property.
You drop in an NSArrayController and bind its Content Array to the
File's Owner.employees. Ok that makes sense, you've bound the
content array of the NSArrayController to the NSMutableArray in your
document, the model, where all the Person's are held. That's the
model connection.
Then you drop an NSTableView onto the document window, plus Add and
Delete buttons. You bind the Value of each of the columns of the
NSTableView to the arrangedObjects.personName and
arrangedObjects.expectedRaise of the NSArrayController .. this sort
of makes sense, that's the data for each column.
The Add button triggers the add: action of the NSArrayController and
the Delete button triggers the remove: action of the
NSArrayController.
'Add' I basically understand. The ArrayController receives an add:,
it makes a new Person, adds it to the end of the MutableArray and by
the magic of bindings the NSTableColumns find out and the
NSTableView gets redrawn.
'Delete' however I don't understand. Hitting the button triggers the
remove: action in the NSArrayController which deletes the selected
entry from the NSMutableArray but ... how does it know which one to
delete? I haven't told the NSArrayController what NSTableView it's
attached to, or if it's attached to one at all. I bound the
NSTableColumns to arrangedObjects.<key> on the NSArrayController,
but that's the wrong way around, and those are the columns anyway,
not the NSTableView itself.
In the previous chapter in the book the exercise was basically to
write something similar by hand, the NSTableView was an outlet of
the controller and when remove: was triggered, you looked up the
current selection using the outlet and knew what to delete, made
total sense. But with the NSArrayController, there's no outlet,
there's no visible binding between the controller and the view, so
how does it know what the current selection is?
If you bind a NSTableColumn to an NSArrayController the NSTableView's
selectionIndexes-binding
is bound automatically to the NSArrayController. (As mentioned in the
Binding Reference: <http://developer.apple.com/documentation/Cocoa/Reference/CocoaBindingsRef/BindingsText/NSTableView.html#//apple_ref/doc/uid/NSTableView-DontLinkElementID_621
>)
Now the NSArrayController selection is in sync with the NSTableView
and remove: makes sense ...
[ Supplementary question - when used in 'hand written' code you
supply a dataSource for the NSTableView. When used with bindings,
that's nil. I wondered how that worked too. If there is a nil
dataSource does the underlying implementation of the NSTableView
assume its NSTableColumns are bound and basically becomes its own
dataSource? ]
You are free to use both (bindings and datasource). Drag'n'Drop for
example …
Cheers,
felix
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